Shares of MannKind (Nasdaq: MNKD) are now up about 10 percent as traders are likely buying the stock as a sympathy play on Arena Pharma (Nasdaq: ARNA). Arena just opened over $12, up more than 35 percent.

Shares of Orexigen (Nasdaq: OREX) are up more than 27 percent and shares of VIVUS (Nasdaq: VVUS) are up more than 9 percent.